Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Sep. 30, 2021 USD ($) security	Dec. 31, 2020 USD ($) security
Fair Value
Less Than 12 Months	$ 147,814	$ 174,022
12 Months or Longer	23,660	23,308
Total	$ 171,474	$ 197,330
Number of Securities | security	50	61
Unrealized Losses
Less Than 12 Months	$ 1,688	$ 977
12 Months or Longer	510	353
Total	2,198	1,330
Fair Value
Less Than 12 Months	588,431	2,561
12 Months or Longer	108	0
Total	588,539	2,561
Unrealized Losses
Less Than 12 Months	8,862	12
12 Months or Longer	1	0
Total	$ 8,863	$ 12
Number of Securities | security	314	4
U.S. Treasury and U.S. government agencies
Fair Value
Less Than 12 Months	$ 15,366	$ 4,966
12 Months or Longer	15,548	17,652
Total	$ 30,914	$ 22,618
Number of Securities | security	8	6
Unrealized Losses
Less Than 12 Months	$ 132	$ 29
12 Months or Longer	423	284
Total	555	313
Mortgage-backed securities, residential
Fair Value
Less Than 12 Months	39,399	84,137
12 Months or Longer	5,728	5,656
Total	$ 45,127	$ 89,793
Number of Securities | security	18	30
Unrealized Losses
Less Than 12 Months	$ 433	$ 471
12 Months or Longer	43	69
Total	476	540
Fair Value
Less Than 12 Months	293,496	2,561
12 Months or Longer	108	0
Total	293,604	2,561
Unrealized Losses
Less Than 12 Months	2,869	12
12 Months or Longer	1	0
Total	$ 2,870	$ 12
Number of Securities | security	79	4
Collateralized mortgage obligations, residential
Fair Value
Less Than 12 Months	$ 66,336	$ 23,858
12 Months or Longer	0	0
Total	$ 66,336	$ 23,858
Number of Securities | security	15	7
Unrealized Losses
Less Than 12 Months	$ 851	$ 22
12 Months or Longer	0	0
Total	851	22
Mortgage-backed securities, multifamily
Fair Value
Less Than 12 Months	1,867	1,943
12 Months or Longer	0	0
Total	$ 1,867	$ 1,943
Number of Securities | security	1	1
Unrealized Losses
Less Than 12 Months	$ 68	$ 0
12 Months or Longer	0	0
Total	68	0
Collateralized mortgage obligations, multifamily
Fair Value
Less Than 12 Months	7,004	2,527
12 Months or Longer	1,402	0
Total	$ 8,406	$ 2,527
Number of Securities | security	4	1
Unrealized Losses
Less Than 12 Months	$ 171	$ 2
12 Months or Longer	33	0
Total	204	2
Asset-backed securities
Fair Value
Less Than 12 Months	14,885	40,690
12 Months or Longer	0	0
Total	$ 14,885	$ 40,690
Number of Securities | security	3	6
Unrealized Losses
Less Than 12 Months	$ 33	$ 225
12 Months or Longer	0	0
Total	33	225
Obligations of states and political subdivisions
Fair Value
Less Than 12 Months		15,901
12 Months or Longer		0
Total		$ 15,901
Number of Securities | security		10
Unrealized Losses
Less Than 12 Months		$ 228
12 Months or Longer		0
Total		$ 228
Fair Value
Less Than 12 Months	294,935
12 Months or Longer	0
Total	294,935
Unrealized Losses
Less Than 12 Months	5,993
12 Months or Longer	0
Total	$ 5,993
Number of Securities | security	235
Corporate bonds
Fair Value
Less Than 12 Months	$ 2,957
12 Months or Longer	982
Total	$ 3,939
Number of Securities | security	1
Unrealized Losses
Less Than 12 Months	$ 0
12 Months or Longer	11
Total	$ 11